1. Field of the Invention
The present invention relates to an air bag apparatus used as a vehicle occupant protecting apparatus.
2. Description of the Related Art
There are two types of conventional steering wheels: a four-spoke type and a three-spoke type. An air bag apparatus as a vehicle occupant protecting apparatus is mounted on the four-spoke steering wheel in many cases. There is also demand, however, for mounting an air bag apparatus on the three-spoke steering wheel. In view of this fact, JP-U 4-137953 discloses an example of a configuration in which an air bag apparatus can be mounted on the three-spoke steering wheel. JP-A 6-328990 discloses a method of folding an air bag by folding back the corners thereof into a trapezoidal form. Further, JP-A 7-89402 discloses an air-bag folding structure, in which the triangular portions of a pentagonally-folded air bag have more folds than the rectangular portions thereof.
The invention disclosed in JP-U 4-137953 will be described below.
As shown in FIG. 15, an air bag apparatus 150 comprises a base plate 152 which is formed substantially trapezoidal in plan view, an inflator 154 mounted on the base plate 152 which eject a gas when the vehicle suddenly decelerates, a bag main body 156 arranged in a folded state on the driver side of the base plate 152, and an air bag pad 158 which is formed substantially trapezoidal in plan view and is mounted on the base plate 152.
As shown in FIG. 16, the air bag apparatus 150 is mounted in such a manner that predetermined spaces 160, 162 are formed between a pair of inclined side walls 152A, 152B of the base plate 152 and a pair of inclined side walls 158A, 158B of the air bag pad 158. A pair of bent portions 156A, 156B of the bag body 156 originally folded in a rectangular form in plan view are inserted into the spaces 160, 162, respectively.
More specifically, as shown in FIG. 17, in order to improve the external design of a three-spoke steering wheel 164, a smoother connection line is demanded among spokes 164A, and 164B extending in the transverse direction of the vehicle and spoke 164C extending in the longitudinal direction of the vehicle. Further, from the standpoint of manufacturing efficiency of the bag body 156, the method of folding the bag body 156 should remain unchanged. Taking these points into consideration, in the above-mentioned structure, the spaces 160, 162 are formed by changing the shape of the base plate 152 and the air bag pad 158 so that the bent portions 156A, 156B of the bag body 156 are inserted into spaces 160, 162, respectively.
However, this structure poses the problem that the bag body 156 cannot be made compact since the inflator 154 has a flat and substantially cylindrical shape and the greater proportion of a top wall 152C of the base plate 152 on which the bag body is mounted is occupied by the inflator 154. In other words, the driver-side portion of the inflator 154 (an upper case 168 side portion formed with gas ejection holes 166) is required to be inserted into an opening (not shown) of the bag body 156, and therefore the bag body 156 is required to be mounted on the base plate 152 so as to cover the upper case 168 of the inflator 154. As the inflator 154 has a flat and substantially cylindrical shape as described above, an attempt to arrange the bag body 156 in a position to cover the inflator 154, the longitudinal and lateral sizes of the bag body 156 unavoidably increases. Therefore the problem that the bag body 156 cannot be made compact arises.
This problem becomes more conspicuous especially in the case where the air bag apparatus 150 is mounted on the three-spoke steering wheel 164.